High-bandwidth Digital Content Protection (HDCP) developed by Intel Corporation provides a digital copy protection approach for digital audio and video content (A/V content) transmitted across cables (e.g., DVI, HDMI) in wired digital systems. HDCP attempts to prevent copy of such A/V content.
An HDCP wireless transmitter device enforces locality on the A/V content by requiring that the Round Trip Time (RTT) between a pair of messages to be no more than 7 milliseconds (ms). This is an attempt to prevent distribution of A/V content beyond a local area network such as a home network.
For locality check between an HDCP transmitter and HDCP receiver, the HDCP transmitter, after initiating the locality check, sets a watchdog timer and waits for 7 ms before which it expects to receive a response from the HDCP receiver. The locality check is performed to ensure that content protection keys can only be exchanged if the RTT is less than 7 ms for point-to-point communication.
However, meeting such RTT may be difficult and unpredictable in a random access wireless network such as a wireless local area network (WLAN) based on the IEEE 802.11 standards (e.g., a Wi-Fi network). For wireless networks where multiple users are accessing the same wireless communication medium, random access delay may be introduced into the RTT. As a result, a locality check using RTT as in HDCP may fail because of random access delays, resulting in long delays for stream set up.